new detection tool for bioavailable copper utilizing transgenic plants carrying recombinant yeast ACE1 transcription factor and GFP reporter genes

Currently, only total copper concentration in soil is normally measured and used as a regulatory standard, despite bioavailable copper in soil being limited due to absorption by soil components. Thus, it is important to distinguish between total copper concentration and bioavailable copper concentration. Unfortunately, a simple, convenient and beneficial tool for detection of bioavailable copper is lacking. In this study, we evaluated some transgenic plants carrying a copper-inducible reporter gene expression system, by transferring them to soil supplemented with various amounts of copper. When supplemented with copper sulfate (CuSO ₄) solution, Green Fluorescent Protein (GFP, reporter) fluorescence was observed at 0.4 mg kg ⁻¹ (weight of copper/weight of soil) or more, but when supplemented with metallic copper, more than 20 mg kg ⁻¹ was required for GFP fluorescence. These results indicated that uptake of copper when supplemented with CuSO ₄ solution is 50 times easier than that when supplemented with metallic copper, and that the transgenic plants respond selectively to bioavailable copper. Sixty independent transgenic plants were generated with different copper detection sensitivity. Thus, the transgenic plant with the optimal target concentration range of bioavailable copper for the intended use can be chosen. This study successfully demonstrates a new transgenic plant-based system is able to detect bioavailable copper without any extraction and purification steps.